Semiconductor logic circuit

ABSTRACT

A current mode type semiconductor logic circuit comprises at least one grounded-emitter transistor through which a power source is connected to the logic circuit. The output of the logic circuit is fed back to the grounded-emitter transistor through a feedback circuit. As a result, the variation in the output of the logic circuit can be controlled to a minimum even when the load of the logic circuit is varied.

Unlted States Patent 1191 1111 3,778,646

Masaki 1 Dec. 11, 1973 [54] SEMICONDUCTOR LOGIC CIRCUIT 3,522,446 8/1970Kodama 307/215 3,539,824 11/1970 Yu et a1 307/215 X 1751 Invent M3,551,836 12 1970 Greeson, Jr.... 330 30 D Sagamlhara-Shl, Japan3,573,488 4/1971 13661111 307/215 x 3,590,274 6/1971 Marley 307/215 [73]Assgnee' Tokyo Japan 3,668,429 1 6/1972 Ainsworth 307 235 R [22] 1972OTHER PUBLICATIONS 1 1 pp N04 222,247 Zakian et al., ElectronicEngineering (Publication); p.

251-253, 4/1966; [30] Foreign Application Pri m Briot, Linear VoltageRegulation Versus Tempera- Feb 5 [971 Japan 46/4229 ture, V01. 13, No.5,p. 1253-1254; 10/1970.

' Patchett, Emitter-follower as a Constant Voltage 52 us. 01 307/215,307/218, 307/237, 5mm, Elem) Engineering (Pub-L 307/264, 307/297,328/175 2/1969; H [5n Int Cl 03k 19/34 03k 5/08, H03k Keller et al.,Current Source Generator, Vol. 12, [58] Field of Search 307/213, 215,218, 11,112031A/1970- 307/235'R, 237, 296, 297, 310, 264; 328/173, 175,146,92; 330/22, 23, 25, 26, Hucke" 28, 40 30 D 69 Asszstant Examiner-L.N. Anagnos Attorney-Craig, Antonelli & Hill [56] References Cited UNITEDSTATES PATENTS [57] ABSTRACT 3 300 658 H1967 Slush a! 307,297 A currentmode type semiconductor logic circuit com- 3,182,269 5/1965 Smith .I.IIIIIIIT330 25 x prises at least one grounded-emitter transistor through3,022,457 2/1962 Doan 330 40 x which a Power Source is connected to the8 Circuit- 3,103,617 9/1963 Schneider et a1.... 307/297 X The output ofthe logic circuit is fed back to the 3,194,985 7/1965 Smith,Jr.et a1.330/30 D grounded-emitter transistor through a feedback cir- 3,259,7617/l96 Nal'ud at al 4 307/297 X cuit. As a result, the variation in theoutput of the logic circuit can be controlled to a minimum even on on 13,515,904 6/1970 Stopper-"\- 307/290 when the load of the logic clrcmtls varied 3,521,086 7/1970 Slob 330/28 X 14 Claims, 6 Drawing FiguresVcc LOAD CKT VEE SEMICONDUCTOR LOGIC CIRCUIT BACKGROUND OF THEINVENTION:

The present invention relates to semiconductor logic circuits and moreparticularly to improvements in a current mode type semiconductor logiccircuit comprising at least one input transistor to which an inputsignal is applied, and at least one reference transistor to which areference signal is applied.

DESCRIPTION OF THE PRIOR ART The semiconductor logic circuits used inhigh speed electronic computers are supposed to satisfy the requirementsof high operating speed, high integration, and low power consumption.

The current mode type semiconductor logic circuit has most generallybeen in use as a high speed logic circuit in the prior art. This type oflogic circuit consumes a large amount of power. To solve this problem, adirect-coupled type logic circuit has been proposed. This logic circuit,however, gives rise to many problems if it is used in a monolithic ICsystem.

SUMMARY OF THE INVENTION An object of the present invention is toprovide a semiconductor logic circuit operable consuming very littlepower and capable of controlling the output-voltage variation to aminimum even if a partial impedance variation occurs in the load circuitnetwork.

Another object of this invention is to provide a semiconductor logiccircuit capable of compensating for the dispersion of circuit elementsand for variations in operating conditions.

Still another object of this invention is to provide a semiconductorlogic circuit capable of driving a transmission line by its collectoroutput even when the logic circuit is fabricated in a monolithic lCsystem.

Briefly, the above objects are realized in a current mode typesemiconductor logic circuit in which a power source is connected to thelogic circuit by way of at least one emitter-grounded transistor, andthe'output of the logic circuit is fed back to the base of theemitter-grounded transistor by way of a feedback circuit.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a circuit diagram showing thefundamental composition of the logic circuit of this invention, and

FIGS. 2, 3(a), 3(b), 4 and 5 are circuit diagrams showing logic circuitsembodying this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there isshown the fundamental arrangement of the logic circuit of thisinvention, wherein the references T,, through T,,, denote transistorsrespectively, to which an input signal Vi(i) is applied, T, atransistor, to which a reference voltage V is applied, and T, agrounded-emitter transistor, through which an emitter source voltage Vis applied to a common emitter terminal E of said transistors T,,through T,,, and T,. The output of a load circuit 1 of the logic circuitcomprising transistors T,, through T,, T is fed back to the base ofgrounded-emitter transistor T via a feedback circuit 2.

In this logic circuit, as is well-known, an OR output or its invertedoutput is obtained at the output terminal 3 according to the result ofcomparison between the reference voltage V and the input signal appliedto the base of one of the transistors T,, through T,,,. According to theteaching of this invention, the output V,,( is fed back to the base ofthe grounded-emitter transistor, thereby minimizing any variation in theoutput voltage of the logic circuit, even if the impedance is partiallyvaried in the load circuit 1. Further objects and advantages of theinvention will be best understood by reference to the followingspecification of illustrative embodiments.

Unless specifically noted, it is assumed that the current amplificationfactor h of the transistor used is sufficiently large, the forwardvoltage drop V across the base and emitter is about 0.8V, and thetransistor is operated unsaturably until its base-collector junction isbiased forward at about 0.5V. This condition is almost fully satisfiedin the ordinary silicon epitaxial planar transistor for logic circuits.

EXAMPLE 1 Referring to FIG. 2, there is shown a logic circuit embodyingthis invention wherein the resistance values of output resistors R, andR are determined to be sufficiently large compared with those ofcollector resistors R and Rap and, hence, a voltage of approximatelyhalf the output voltage is produced at theconnection point 4 of R, and R'wheri transistor T, or T is conducting. This voltage is applied to thebase of a transistor T The emitter of transistor T, is connected to thebase of a grounded-emitter transistor T and an emitter source voltage VE5 is applied to the emitter of transistor T, by way of resistor RBecause the base-emitter voltage V of transistors T and T is constant,the voltage V, at the connection point of the output resistors R, and Ris given as V V ZV I 2 X Therefore, the output voltage V, at thecollector on the side of whichever transistor T, or T is conducting isex pressed as In this current mode type semiconductor logic circuitcomprising transistors T, and T the output voltage V,, is determinedessentially by the emitter source voltage V on condition that theresistance. values of the load resistors R and R are sufficientlysmaller than those of the output resistors R, and R even if smallvariations occur in the value of the load resistors R and Rcp. Underthis condition, therefore, the output voltagev can be kept minimallyaffected by the variation inthe load impedance. By suitably determiningthe value of a capacitor C inserted in the base of transistor T anoutput voltage with the desired waveform can be obtained.

EXAMPLE 2 In FIG. 3(a), an output resistor R, is connected across thecollectors of transistors T, and T and one end of resistor R, isconnected to the base of a groundemitter transistor T In this circuit,when the transistor T, is in the conducting state, the base current ofgrounded-emitter transistor T which current flows via the outputresistor R,, is sufficiently small. Therefore,

the collectors of transistors T and T and the base of transistor T areat nearly the same potential.

Hence, the output voltage V obtainable at conduction of transistor T isgiven as EXAMPLE 3 This example, as shown in FIG. 3(b), is similar toExample 2, except that this circuit makes an ON output available.

EXAMPLE 4 This example, as shown in FIG. 4, is a modification ofExample 1. In FIG. 4, the input signal is applied to the base oftransistors T through T This circuit is characterized by its capabilityof delivering a large amplitude output.

EXAMPLE 5 This example is shown in FIG. 5 wherein a stabilizing circuitusing an emitter source voltage V provided as in Example 2 is employedto compensate for dispersion or temperature variation in V ie, ctc., ofthe transistors. The aim of this stabilizing circuit is to make theoutput voltage of transistor T equal to the voltage determined only bythe value of the source voltage V and the ratio of the values ofresistors R and R when transistor T is in the conducting state.

In the stabilizing circuit (indicated by the dotted line), the output ofa differential amplifier comprising transistors T T resistors R and R isapplied to a transistor T via a transistor T and a resistor R Therefore,the collector voltage of transistor T (i.e., the emitter source voltageV can be made equal to the emitter voltage of transistor T Hence, if thevalues of transistors T and T, are determined to be nearly the same, andlikewise the values of resistors R and R,, and also the value ofresistor R is determined so that the collector current of T is nearlyequal to that of transistor T the emitter voltage of transistor T namelythe emitter source voltage V is stabilized. The purpose of thetransistor T is to approximate the operating conditions of twotransistors T and T It is to be noted that resistance and voltage valuesindicated in the drawings are only for reference; the invention is notlimited to those values. The transistors used in the foregoingembodiments may be of either npn or pnp.

In the conventional current mode type semiconductor logic circuitfabricated in a monolithic IC system, the ratio of resistance values canbe relatively accurately controlled within the same monolithic circuit.Hence, the accuracy of the output voltage can be con- 6 trolled to befairly high if the emitter resistor and collector load resistor areformed in the same monolithic circuit. In a monolithic circuit, however,it is difficult to reduce the dispersion of the absolute value ofresistance. When the collector load resistor is not included in the samemonolithic circuit but is connected thereto externally, the accuracy ofthe output voltage is significantly lowered. This will result insaturation of the circuit, to lower the operating speed and reduce thenoise margin. In a large electronic computer, it is necessary tominimize the delay caused by elongated length of a transmission line. Tothis effect the distributed line for transmission must be terminated bya resistor whose characteristic impedance is nearly equal to that of thedistributed line network. In such case it is apparently impossible forone monolithic circuit to include both the emitter resistor and thecollector load resistor; here the aforementioned problem is inevitable.

Whereas, according to this invention, as described above, variations inthe output voltage can be controlled to a minimum even when partialimpedance variation takes place in the load circuit network of thecollector. Thus, in other words, the invention enables the use of amonolithic IC system to manufacture efficient logic circuits free of theprior art problems.

I claim:

1. In a current mode type semiconductor logic circuit having at leastone input transistor to which an input signalv is applied, at least onereference transistor to which a reference signal is applied, said inputtransistor being adapted so as to operate when said input signal islarger than said reference signal, a power source, and a load circuitconnected to said input and reference transistors for deriving outtherefrom an output signal from said input and reference transistors,the improvement which comprises at least one grounded emitter transistorthrough which said power source is connected to said input and referencetransistors, and a feedback circuit connected between said load circuitand said grounded emitter transistor for feeding back said output signalthereto.

2. A logic circuit according to claim 1, wherein said feedback circuitcomprises output resistor means connected between the outputs of saidinput and reference transistors, and a grounded collector transistorconnected between said output resistor means and the input of saidgrounded emitter transistor.

3. A logic circuit according to claim 1, wherein said feedback circuitcomprises an output resistor connected between the outputs of said inputand reference transistors, and said grounded emitter transistorconnected to said output resistor.

4. A logic circuit according to claim 1, which comprises a stabilizingcircuit connected between said grounded emitter transistor and saidpower source for stabilizing the emitter voltage of said groundedemitter transistor.

5. A current mode type semiconductor logic circuit comprising:

at least one input transistor to which an input signal is to be applied;

a reference transistor to which a reference signal is to be applied,said input and reference transistors being coupled together in commonfor receiving a source of power;

a load means connected to each of said input and reference transistorsfor generating a signal when said input signal is larger than saidreference signal;

a power coupling transistor, having its emitter connected to said sourceof power, connected to the common connection point of said input andreference transistors for coupling thereto said source of power; and

means connected between said load means and power coupling transistor,for feeding back the output of said load circuit to said power couplingtransistor, so as to compensate for variations in the output of saidlogic circuit.

6. A current mode type semiconductor logic circuit according to claim 5,wherein said feedback means comprises means for resistively connectingthe output of said load means to said power coupling transistor.

7. A current mode type semiconductor logic circuit according to claim 6,wherein said feedback means comprises first and second resistorsconnected in series between said input and reference transistor outputs,and a feedback transistor coupling the common connection of said firstand second resistor to said power coupling transistor.

8. A current mode type semiconductor logic circuit according to claim 7,wherein said at least one input transistor comprises a first inputtransistor to which said input signal is applied and a second inputtransistor connected to the output of said first input transistor and tosaid reference and said power coupling transistor, the output of saidsecond input transistor being connected to said load means.

9. A current mode type semiconductor logic circuit according to claim 6,wherein said feedback means comprises a resistor connected between saidinput and reference transistors and a conductor for coupling the outputof one of said input and reference transistor to said power couplingtransistor.

10. A current mode type semiconductor logic circuit according to claim9, wherein said conductor is connected to said input transistor.

11. A current mode type semiconductor logic circuit according to claim9, wherein said conductor is connected to said reference transistor.

12. A current mode type semiconductor logic circuit according to claim8, further comprising a stabilizing circuit connected between said powersource and said power coupling transistor for compensating for variationin the characteristics of said transistors.

13. A current mode type semiconductor logic circuit according to claim12, wherein said stabilizing circuit comprises a differential amplifiercircuit having one of its inputs coupled to said power couplingtransistor and the other coupled to a compensating power supply circuit,the output of said differential amplifier being connected through a pairof transistors to said power coupling transistor.

14. A current mode type semiconductor logic circuit according to claim13, wherein said compensating power supplying circuit comprises a pairof transistors connected in series, the characteristics of one of whichcorresponds substantially to said power coupling transistor and abiasing transistor connected between said power source and said onetransistor of said pair for maintaining the collector current thereofsubstantially the same as the collector current of said power couplingtransistor.

1. In a current mode type semiconductor logic circuit having at leastone input transistor to which an input signal is applied, at least onereference transistor to which a reference signal is applied, said inputtransistor being adapted so as to operate when said input signal islarger than said reference signal, a power source, and a load circuitconnected to said input and reference transistors for deriving outtherefrom an output signal from said input and reference transistors,the improvement which comprises at least one grounded emitter transistorthrough which said power source is connected to said input and referencetransistors, and a feedback circuit connected between said load circuitand said grounded emitter transistor for feeding back said output signalthereto.
 2. A logic circuit according to claim 1, wherein said feedbackcircuit comprises output resistor means connected between the outputs ofsaid input and reference transistors, and a grounded collectortransistor connected between said output resistor means and the input ofsaid grounded emitter transistor.
 3. A logic circuit according to claim1, wherein said feedback circuit comprises an output resistor connectedbetween the outputs of said input and reference transistors, and saidgrounded emitter transistor connected to said output resistor.
 4. Alogic circuit according to claim 1, which comprises a stabilizingcircuit connected between said grounded emitter transistor and saidpower source for stabilizing the emitter voltage of said groundedemitter transistor.
 5. A current mode type semiconductor logic circuitcomprising: at least one input transistor to which an input signal is tobe applied; a reference transistor to which a reference signal is to beapplied, said input and reference transistors being coupled together incommon for receiving a source of power; a load means connected to eachof said input and reference transistors for generating a signal whensaid input signal is larger than said reference signal; a power couplingtransistor, having its emitter connected to said source of power,connected to the common connection point of said input and referencetransistors for coupling thereto said source of power; and meansconNected between said load means and power coupling transistor, forfeeding back the output of said load circuit to said power couplingtransistor, so as to compensate for variations in the output of saidlogic circuit.
 6. A current mode type semiconductor logic circuitaccording to claim 5, wherein said feedback means comprises means forresistively connecting the output of said load means to said powercoupling transistor.
 7. A current mode type semiconductor logic circuitaccording to claim 6, wherein said feedback means comprises first andsecond resistors connected in series between said input and referencetransistor outputs, and a feedback transistor coupling the commonconnection of said first and second resistor to said power couplingtransistor.
 8. A current mode type semiconductor logic circuit accordingto claim 7, wherein said at least one input transistor comprises a firstinput transistor to which said input signal is applied and a secondinput transistor connected to the output of said first input transistorand to said reference and said power coupling transistor, the output ofsaid second input transistor being connected to said load means.
 9. Acurrent mode type semiconductor logic circuit according to claim 6,wherein said feedback means comprises a resistor connected between saidinput and reference transistors and a conductor for coupling the outputof one of said input and reference transistor to said power couplingtransistor.
 10. A current mode type semiconductor logic circuitaccording to claim 9, wherein said conductor is connected to said inputtransistor.
 11. A current mode type semiconductor logic circuitaccording to claim 9, wherein said conductor is connected to saidreference transistor.
 12. A current mode type semiconductor logiccircuit according to claim 8, further comprising a stabilizing circuitconnected between said power source and said power coupling transistorfor compensating for variation in the characteristics of saidtransistors.
 13. A current mode type semiconductor logic circuitaccording to claim 12, wherein said stabilizing circuit comprises adifferential amplifier circuit having one of its inputs coupled to saidpower coupling transistor and the other coupled to a compensating powersupply circuit, the output of said differential amplifier beingconnected through a pair of transistors to said power couplingtransistor.
 14. A current mode type semiconductor logic circuitaccording to claim 13, wherein said compensating power supplying circuitcomprises a pair of transistors connected in series, the characteristicsof one of which corresponds substantially to said power couplingtransistor and a biasing transistor connected between said power sourceand said one transistor of said pair for maintaining the collectorcurrent thereof substantially the same as the collector current of saidpower coupling transistor.